Why the study?
How do heart sound dynamics and ventricular asynchronism differ among patients with right bundle-branch block, left bundle-branch block, and normal subjects?
How do heart sound dynamics and ventricular asynchronism differ among patients with right bundle-branch block, left bundle-branch block, and normal subjects?
This study demonstrates that the first heart sound is delayed in LBBB but not RBBB, confirming its exclusive left-sided origin.
Answers are grounded in this paper and cite their sources.
Refines S1 interpretation in bundle branch block; confirms left-sided origin but observational data leave clinical utility open.
A clinical, electrocardiographic, phonocardiographic, and arteriographic study was made of 20 normal subjects, 20 patients with right bundle-branch block (RBBB) and 20 patients with left bundle-branch block (LBBB). Ventricular asynchronism was documented in nearly all cases of bundle-branch block by the behavior of the arterial pulse and the heart sounds. The first heart sound was of normal duration in all cases and usually had the normal number and position of its three components. The first sound had a normal relationship with the QRS component of the electrocardiogram in RBBB, but its onset was markedly delayed in LBBB. This fact confirms the exclusive left-sided origin of the first sound. The third (or ejection) component of the first sound had a greater delay in LBBB, due to intraventricular block, and this delay was closely related to that of the carotid pulse rise. Reversed splitting of the second sound in LBBB was common.
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Oravetz et al. (1967) studied this question.
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